Exemplary embodiments pertain generally to manufacture of heat exchanger tubes and, more particularly, to the removal of residual solvent from a prelubricant applied to heat exchanger tubes during the manufacturing process.
Tube coil heat exchangers are commonly used in many industrial applications wherein it is desired to transfer heat from one fluid to another fluid, one fluid passing through the heat exchange tubes and the other fluid passing over the heat exchange tubes. For example, evaporators, condensers, and other heat exchanger of various heating, ventilating and air conditioning and refrigeration (HVAC&R) equipment are conventionally tube coil heat exchangers. Typically, a plurality of fins are mounted to the heat exchange tubes forming the tube coil heat exchanger.
In manufacturing such tube coil heat exchangers, the heat exchange tubes are passed through holes punched in the fin sheet. Each hole is surrounded by a collar of sheet material formed when the holes for receiving the tubes are punched in the fin sheet. To ensure intimate contact between the fins and the exterior surface of the heat exchange tubes, it is customary, after the fins have been assembled onto the heat exchange tubes to force a mandrel through each heat exchange tube. The mandrel is sized to cause the heat exchange tube to expand radially outward thereby establishing intimate contact between the exterior surface of tube and the fin collars circumscribing the tubes.
When manufacturing finned tube coil heat exchangers with aluminum or aluminum alloy tubes, it is conventional practice to lubricate the interior of the tubes prior to forcing the mandrel through the tube. Proper lubrication of the inside of the tube is necessary due to the high coefficient of friction characteristic of aluminum and aluminum alloy tubes. One method of prelubricating the tubes is to apply a dry lubricant carried in a liquid solvent, typically a volatile organic compound, to the inside surface of the tube. After the lubricant has been applied, it is necessary to remove the solvent, thereby leaving a residual wax-like film coating the inside surface of the tubes.
The conventional practice for removing the liquid solvent from the inside surface of the tube, is to blow dry air through the tube while heating the lubricated tube to a temperature above the boiling point of the solvent for a sufficient period of time to ensure that all the solvent has been evaporated and the solvent vapors carried away by the air passing through the tube. It is important that all the solvent be removed as the presence of solvent is detrimental to the performance of the lubricant in facilitating the subsequent passage of the mandrel through the tube during the tube expansion process. Thus, care must be taken to ensure complete evaporation of the solvent. Further, such volatile organic compounds are flammable and the temperature to which the tube must be heated is generally above the flash point of the solvent. Therefore, care must be taken to properly exhaust the solvent vapors away and avoid reaching the flammable limits. Conventionally, the solvent vapors are simply exhausted to the atmosphere or incinerated.